To address the uncertainty of the workpiece volume and the mechanical and hydraulic dynamic coupling of the test system during the test process, firstly, the multi-dynamic coupling of the pressure pulse fatigue test system is decoupled and downgraded by means of singular value uptake theory. Secondly, the compensation of the downgraded error and volume uncertainty of the system is achieved by using the active disturbance rejection control algorithm, so as to ensure the accurate tracking of the pressure output of the test system to the command signal. Finally, the stability and error convergence of the active disturbance rejection control algorithm based on the simplified model are theoretically and quantitatively analyzed. The feasibility and validity of the control method are verified by co-simulation and experiment. The results show that the active disturbance rejection control algorithm based on the reduced-order model has good robustness to the variation of workpiece volume parameters in the pressure pulse test system and can effectively estimate and compensate for the disturbances such as the reduced-order error of the system model, and its tracking performance is improved by up to 35.4% compared with that of the PID controller.